YOUR = possessive, something belongs to you
YOU'RE = you are

THERE = referring to a place
THEIR = possessive, something belongs to them
THEY'RE = they are

GREAT = good
GRATE = to shred something

"When you're writing dialogue," Lena explained, "You need a new paragraph every time a new person speaks."

"Are you sure?" The reader asked, racking their brains to try and remember the format of their dialogue-heavy scenes.

"Absolutely," Lena replied. "Otherwise, the sentences get jumbled together and you don't know who is saying what. It really takes away from your story."

( lena! )